Although you should focus on road signs more than you do the app, there could be a dangerous situation in which the app says "make a left turn at the light", but before reaching the light there is a railroad crossing. Of course you need to stop at that, but the app can enhance the situation but treating it like another instruction. I see no problem here but an overall safety enhancement.
If that isn't to become some sort of text-to-speech database dump about the area, there has to be a good theory of the conditions for what's worthwhile. And I sense that the natural conditions are the same as the conditions for putting up warning signs, reducing the speed limit, etc.
This can have the potential effect that people expect the apps to always announce a crossing. So when the app fails to announce for whatever reason, people go through the crossing and get hurt.
b) they have been proven to not having taken action even though "safety advocates" have asked for years.
c) as such they are ripe for some cherry picked court to fine them
There are many many warnings we encounter in daily life which only exist to protect not just the consumer but the manufacturer or service provider from unscrupulous lawyers and political officials who would otherwise exploit the situation.
no snark intended, however we live in a society where someone else is always to blame and usually someone with money which can be taken by penalty or forfeiture in trial or settlement.
A driver needs to stop at a railroad crossing just like they do at a red light or stop sign. If a driver is ignoring any of these, I really don't see how an app is going to help.
Or conversely, if a crossing is somehow not well-marked on the road then that's deep negligence on the part of the transportation department and it needs to be fixed -- it has nothing to do with apps. (All the crossings I know have a closed gate and flashing lights, although I understand this might vary locally.)